Numerical Simulation of Severe Water Ingress Accidents in a ModularHigh Temperature Gas Cooled Reactor

Zhang, Z.; Scherer, Winfried

Report

FZJ-2016-05949

Numerical Simulation of Severe Water Ingress Accidents in a ModularHigh Temperature Gas Cooled Reactor

Zhang, Z. ; Scherer, W.FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3180, 127 p. (1996)

Please use a persistent id in citations: http://hdl.handle.net/2128/12729

Report No.: Juel-3180

Abstract: This report analyzes severe water ingress accidents in the SIEMENS 200MW Modular Pebble-Bed High Temperature Gas Cooled Reactor (HTR-MODULE) under the assumption of no active safety protection systems in order to find the safety margins of the current HTR-MODULE design and to realize a catastrophe-free nuclear technology. A water, steam and helium multi-phase cavity model is developed and implemented in the DSNP simulation system. The DSNP system is then used to simulate the primary and secondary circuit of a HTR-MODULE power plant. Comparisons of the model with experiments and with TIN1M calculations serve as validation of the simulation. The analysis of the primary circuit tries to answer the question how fast the water enters the reactor core. It was found that the maximum H$_{2}$O concentration increase in the reactor core is smaller than 0.3 kg/(m$^{3}$s) The liquid water vaporization in the steam generator and H$_{2}$O transport from the steam generator to the reactor core reduce the ingress velocity of the H$_{2}$O into the reactor core. In order to answer the question haw much water enters the primary circuit, the full cavitationof the feed water pumps is analyzed. It is found that if the secondary circuit is depressurized enough, the feed water pumps will be inherently stopped by the full cavitation. This limits the water to be pumped from the deaerator to the steam generator. A comprehensive simulation of the MODUL-HTR power plant then shows that the H$_{2}$O inventory in the primary circuit can be limited to about 3000 kg. The nuclear reactivity increase caused by the water ingress leads to a fast power excursion, which, however, is inherently counterbalanced by negative feedback effects. Concerning the integrity of the fuel elements, the safety relevant temperature limit of 1600 °C was not reached in any case.

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